The present invention relates generally to a lift device and more specifically to a lift device for an industrial vehicle which is equipped with a guide mechanism for guiding a hose.
In a forklift truck as an industrial vehicle, its lift bracket may be equipped with various kinds of attachments which are designed to perform different kinds of operations. In this case, hydraulic piping is needed for supplying hydraulic fluid for actuating the attachment.
A conventional lift device for an industrial vehicle is disclosed in Japanese Patent Application Publication No. 2002-20087. The lift device for the industrial vehicle (hereinafter referred to merely as “lift device”) is a lift device for a three-stage mast forklift truck. The lift device has a hydraulic cylinder located between the spaced masts. At the top end of the piston rod of the hydraulic cylinder is supported a pulley which has two grooves for guiding a chain and a hose, respectively. The chain is connected to a lift bracket and wound around the pulley along one of the grooves. The hose which is used for supplying hydraulic fluid to an attachment installed on the lift bracket is wound around the pulley along the other groove. The lift bracket is movable up and down relative to the masts according to the extension and the retraction of the piston rod. While the lift bracket are moved up and down, the pulley guides the chain and the hose. In this case, the hose and the chain are reversibly moved while being guided by the pulley.
The lift device provides a good front view to an operator of the vehicle. However, this advantage is limited to the front view in lateral directions, and the pulley at the top end of the piston rod obstructs the front view of the operator in vertical direction. Further improvement of the front view may be accomplished, for example, by reducing the pulley diameter. However, the reduction of the pulley diameter is limited because of the restriction by mechanical properties of the hose, performance of hydraulic control and the like. In a vehicle having full free lift masts, a distance for which the lift bracket is raised without raising the masts is defined as a free lift distance. When the pulley is provided on the top end of the piston rod, the free lift distance is reduced by the length corresponding to the diameter of the pulley.
The problems with the lift device of Japanese Patent Application Publication No. 2002-20087 are solved by a lift device which is disclosed in Japanese Patent Application Publication No. 2004-359445. The lift device for an industrial vehicle according to this Publication includes a guide pulley which is provided on a lateral side of the upper end portion of the piston rod of the hydraulic cylinder for guiding a chain, a lift bracket which is connected to the chain wound around the pulley and operable to rise and lower through the pulley according to the extension and the retraction of the piston rod, and a plurality of hoses for supplying hydraulic fluid to an attachment installed on the lift bracket. A plate-like roller-mounting member is provided on the top of the upper end portion of the piston rod, and a plurality of guide rollers are mounted on the roller-mounting member for guiding the plurality of hoses. Each guide roller has guide grooves formed with a curvature, and the hoses are received in and wound around the guide grooves. The guide rollers are rotatable and arranged along an arc, thereby guiding the hoses in a state curved along the guide grooves. The grooves of each guide roller serve to prevent the hoses from falling off from the guide rollers. The lift device which uses the plurality of guide rollers in place of a pulley for guiding the hoses solves problems of the life device disclosed in Japanese Patent Application Publication No. 2002-20087 concerning the vertical front view and the free lift distance.
In the lift device of Japanese Patent Application Publication No. 2004-359445, however, the hoses which are guided by the plurality of guide rollers are inevitably placed in point contact therewith. Such point contact between each hose and each guide roller produces local contact pressure against the hose, which may damage the hose. Since the plurality of guide rollers guide the hoses while in point contact therewith, the hoses tend to be guided in such a manner that they climb over each guide roller and, therefore, the hoses are not guided smoothly. Furthermore, since the diameter of the guide rollers is small, the guide rollers rotate at a high speed in guiding the hoses, so that the hoses tend to slip easily relative to the guide rollers and the surfaces of the hoses may be damaged, accordingly. Replacing the damage hose with a new one is a laborious and time-consuming work because the hydraulic fluid in the hose must be removed before the hose is removed for the replacement. Additionally, hydraulic fluid or oil may leak accidentally from the hose during the above replacement work thereby to impair the working environment. Thus, the frequency of replacing the hose need be reduced as much as possible by preventing the hose from damage.
The present invention is directed to a lift device for an industrial vehicle which prevents the damage to a hose which is guided by a guide mechanism which dispenses with a pulley.